1. Field of the Invention
The present invention relates to a pile driving system for driving piles into an underwater surface; and more particularly, the present invention relates to a pile driving system capable of being used in great depths of water.
2. Description of the Prior Art
In the installation of an offshore structure, such as a drilling or production platform, it is the general practice to secure the structure in some manner to the underwater surface to prevent overturning of the structure. A conventional technique for securing the offshore structure to the ocean floor is the driving of elongated piles into the underwater surface. Typically, an offshore structure will have several legs to support the structure, with one or more piles being provided at each leg depending upon the type of soil into which the piles are to be driven. Generally, piles will be carried in pile sleeves attached to the outside of the support legs, or will be lowered through the interior of the hollow support legs until the piles contact the underwater surface. Examples of the foregoing techniques are found in U.S. Pat. No. 3,751,930, issued Aug. 14, 1973, to Mott et al., and U.S. Pat. No. 3,604,522, issued Sept. 14, 1971, to Doughty, respectively.
Many pile driving hammers have been proposed in the past. These proposed hammers fall into two basic categories: those which are operated above the water surface and those operated fully underwater. Examples of the former category are shown in the Mott et al. patent and U.S. Pat. No. 3,289,420, issued Dec. 6, 1966, to Guy. Examples of the latter category are described in U.S. Pat. Nos. 3,646,598, issued Feb. 29, 1972, to Chelminski; 3,750,609, issued Aug. 7, 1973, to Chelminski; 3,842,917, issued Oct. 22, 1974, to Wisotsky; 3,817,335, issued June 18, 1974, to Chelminski; 3,846,991, issued Nov. 12, 1974, to Wisotsky; and the Doughty patent. Another underwater hammer is the HYDROBLOCK.TM., manufactured by Hollandsche Beton Maatschappij bv of the Netherlands.
Those hammers which operate above the water surface are typically of conventional construction, wherein either compressed air or steam provides the motive force which causes the hammer to deliver repetitive blows to the pile. A distinct disadvantage in employing hammers of this type is the necessity of utilizing pile followers in order to transmit the forces from the hammer to the top of the pile. A pile follower is an extension that is attached to the top of the pile and the pile follower is struck by the hammer. Particularly when driving piles in great depths of water, a plurality of these followers are necessary. Followers have several disadvantages, in that they are extremely heavy, expensive, and believed to introduce inefficiency into the pile driving system because of energy losses associated with transmitting the hammer's blow through the follower to the upper end of the pile. Additionally, the utilization of a plurality of pile followers results in a substantial amount of time wasted while the followers are brought into place and connected to the previous follower. In many locations throughout the world, weather conditions are such that pile driving operations cannot be accomplished throughout the year, but only during certain portions of the year when the ocean is relatively calm and fair skies prevail. Accordingly, if the offshore structure cannot be secured to the underwater surface during which time the weather conditions are favorable, the offshore structure must remain idle until such time as better weather conditions prevail. Since these offshore structures are most typically used to facilitate the drilling of offshore oil wells, the time delays result in lost crude oil, or natural gas, production, along with the risks attendant in not having the offshore structure fully secured to the underwater surface.
Another disadvantage inherent in utilizing a plurality of pile followers is that fairly large derrick barges must be used in the pile driving operation to support the hammer and the pile followers during the pile driving operation and while connecting the pile followers. Furthermore, additional costs are associated with the pile driving operation since, in addition to the initial cost of the pile followers, there are costs associated with transporting and storing them until their use is necessitated.
Accordingly, these disadvantages prompted the introduction of pile driving hammers which are operated while being fully underwater, whereby the hammer could directly contact the pile and eliminate the utilization of the followers. The previously proposed underwater hammers still present many disadvantages which militate against, and indeed even prevent, their use in deep water offshore pile driving operations.
Generally, these underwater pile driving hammers lack any means for positioning the hammer above the pile which is to be driven into the underwater surface; e.g., the hammers shown in the Wisotsky patents and the U.S. Pat. No. 3,750,609 to Chelminski, and the HYDROBLOK.TM. hammer. In the case of the Chelminski U.S. Pat. No. 3,750,609, the hammer is mated with an anchor to form a unit, and this unit is merely lowered into the water until the underwater surface is reached. It is believed that this hammer system could not be utilized in operations wherein precise locating of the anchor is necessary. The Wisotsky patents disclose underwater hammers which, it is believed, could not be utilized for driving piles in the great depths of water prevalent at many offshore locations, since no means is provided for guiding the hammer into accurate alignment with a prepositioned pile which is already located at the underwater surface. It would appear that these hammers could only be utilized in situations wherein after the pile has been placed in contact with the underwater surface, the top of the pile either extends above the water surface, or is disposed a short distance below the water surface, such that an operator disposed upon a derrick barge could visually guide the hammer into engagement with the pile, or divers disposed in the water could guide the hammer into engagement with the top of the pile.
Although the HYDROBLOK.TM. hammer has a sleeve at its base for engaging the top of a pile, there is no means provided for guiding the HYDROBLOK.TM. hammer into engagement with the top of a pile which may be located many hundreds of feet below the water surface. Additionally, the HYDROBLOK.TM. hammer employs a ram and hydraulic power unit contained in a casing which is purged of water by air pressure. The casing must be provided with sufficient ballast to counteract the buoyancy of the casing. Accordingly, although this hammer is adapted for underwater operations, it is thought to be only used above the water in conjunction with conventional pile followers or used in very shallow depths of water wherein divers may position the hammer upon the top of a pile.
The Chelminski U.S. Pat. Nos. 3,817,335 and 3,646,598 disclose underwater hammers which are employed within the interior of hollow piles, whereby the pile itself guides the hammer into a position whereby the pile may be driven into the underwater surface. The major disadvantage of this approach is that the overall length of the pile must closely approximate the distance between the water surface and the underwater surface, whereby the hammer will be guided into a pile driving relationship with respect to the interior of the hollow pile. Accordingly, in deep water operations these hammers cannot be readily utilized unless a plurality of hollow piles are welded together to form a continuous guide for the hammer, and this approach inherently has the disadvantages which are present when utilizing conventional pile followers.
The Doughty hammer is similar to the Chelminski U.S. Pat. Nos. 3,817,335 and 3,646,598, in that it relies upon the inner surface of a hollow support leg of the offshore structure to guide it into engagement with the top of the pile to be driven into the underwater surface. Were this hammer to be utilized to drive a pile disposed along the lower, outer surface of a support leg of an offshore structure, it would encounter the same difficulties of previously described hammer systems, in that it could not be accurately aligned to engage the top of the pile. Another disadvantage and potential hazard to the system proposed by Doughty results from its construction. The Doughty system utilizes a casing having an integral anvil at its lower end. As a ram, which is contained within the casing, repeatedly strikes the anvil, the casing will be continually pulled into tension. It is believed that the casing will fracture, thus causing the anvil to separate from the casing.
Accordingly, prior to the development of the present invention, there has been no pile driving system for driving piles into an underwater surface, particularly underwater surfaces disposed at great depths, which is capable of being easily and inexpensively brought into engagement with the top of the pile whereby the offshore structure can be quickly secured to the underwater surface. Therefore, the art has sought a pile driving system for driving piles into an underwater surface which easily and inexpensively drives the piles into the underwater surface, absent the problems of previously proposed hammer systems and without the necessity of pile followers.